Evacuated electric discharge vessel



June 23, 1936. S ITHE L 2,045,561

EVACUATED ELECTRIC DISCHARGE VESSEL Filed Aug. 28, 1933 ITTOR/VEV.

Patented June 23, 1936 UNITED STATES PATENT OFFICE Colin JamesSmithelis, Bushey, England, assignor to The M-O Valve Company Limited,London,

England Application August 28, 1933, Serial No. 687,158 In Great BritainSeptember 1, 1932 3 Claims.

This invention relates to evacuated electric discharge vessels of thetype in which one electrode (hereinafter called the anode) forms part ofthe envelope.

In the larger vessels of this type, consuming more than 1,000 watts, theanode is usually cooled by the forced circulation of fluid. In thesmaller vessels of the type, consuming less than 20 watts, no specialcooling means is usually provided. Between these extremes areintermediate vessels, consuming power of the order of 50 watts, in whichthe anode may be cooled suitably by the attachment of fins withoutforced circulation of fluid. The invention relates more particularly tovessels of this intermediate class.

The anodes of such vessels, like those of the smaller class but unlikethose of the larger class, are often cylinders whose-cross sectiondeparts widely from the circular form, being for example lozenge-shaped.Anodes of non-circular cross section will here be termed flattened. Inorder to prevent the collapse of a flattened anode when evacuated, thematerial of which it is made has generally to be thicker than would benecessary if the cross-section were circular and often thicker than isdesirable on other grounds. The object of this invention is to combinethe provision of cooling means with the provision of supporting meansthat enables thinner material to be used.

In the accompanying drawing, Figure 1 shows diagrammatically a sideelevation of an electric discharge device provided according to theinvention, with a cooling sheath, the anode and sheath in this elevationbeing shown as a section on the line l-l of Figure 2; Figure 2 shows afront elevation of the electric discharge device and cooling sheathshown in Figure l; and Figure 3 shows a transverse section on the line3-3 in Figure 2 of the cooling sheath and anode only, showing the formof the cooling fins in this particular example and the approximaterelative positions of the anode and the interior surface ofthe coolingsheath.

In the drawing, the flattened anode I and the glass portion 2 form theenvelope of the discharge device, which is evacuated in known mannerthrough an evacuating tube l sealed into the pinch tube 8. Theelectrodes are supported by the pinch 9 and by insulatingplates 3bearing against the electrodes and the interior surface of the anode.The grid electrode 4 is shown in Figure 1.

According to the invention, a sheath 5 is provided for the anode andthis sheath is provided,

as shown, with cooling fins 6'. The sheath is shown in Figure 3 as beingtight against the anode at the ends of its maximum diameter of itscross-section and exerts pressure on the anode, that is, it grips theanode, along this line, while the sheath is shown as closely approachingthe anode at other parts of its surface.

According to the invention in an electric discharge vessel of the typedescribed having a flattened anode, the anode is supported againstcollapse under external pressure by being gripped in a cooling sheath.

A little explanation is necessary to explain what is implied here by theword "gripped. When a flattened anode collapses under pressure, thedecrease of one of the dimensions of its cross-section is generallyaccompanied by the increase of some other dimension. In general, thedimension that increases will be the maximum dimension. There maypossibly be exceptions to this statement, especially if the crosssection has several equal maximum dimensions (for example if it is asquare), but if there are exceptions, they are excluded from the scopeofthe invention, which applies only to anodes such that collapse underpressure is accompanied by increase in one at least of the maximumdimensions. Collapse can then be prevented by preventing increase ofthis maximum dimension. The sheath is said to grip the anodewhen itexerts a pressure on the anode along the maximum dimensions of itscross-section and thus prevents its increase.

The sheath has not only to support the anode but it has also to cool it;accordingly it must be in efiective thermal contact with the anode. Forthis purpose, it must just touch or approach very closely to the anodeover the greater part of its cross-section, while exerting pressure onit only along lines in the neighbourhood of its maximum dimension. Theseconditions can be fulfilled at the same time by giving to the internalcross-section of the sheatha perimeter slightly greater than theperimeter of the cross-section of the anode, but making that dimensionof the cross-section of the sheath which is to coincide with the maximumdimension of the anode slightly less than this dimension. If the mostperfect thermal contact and the least distortion of the anode arerequired, the diflerences implied by the word slightly in the precedingsentence may be of the order of one mil; but of course either of themmay be greater if the corresponding quality is sacrificed.

In order that a sheath should be a cooling sheath within the meaning ofthis specification,

it is necessary only that with a given temperature,

difference it should transfer to any fluid in which it is immersedsubstantially more heat than would be transferred by the unsheathedanode under the same temperature difference. Thus, being made of metal,it might be similar to the anode in external form, but have thick wallsand a larger surface. But generally it will be convenient to make thesheath as thin as is consistent with the rigidity necessary to avoiddistortion by its reaction with the anode, and to provide its exteriorsurface with fins. Aluminium is a suitable material for the coolingsheath; a convenient method of making large numbers of sheaths to theclose dimensions required is to extrude a long length .of the desiredcross-section and then cut it into the lengths appropriate for theindividual anodes; the fins must then, of course, be longitudinal.

The sheath may be placed round the anode by.

heating it and shrinking it on; if the anode is supported on a glassseal, this method is usually preferable to forcing the sheath on. Theanode is most likely to collapse when itis hot, for then the metal isweakest. It will be necessary therefore to provide the anode withsupport during baking. This may be achieved by fitting the sheath on theanode before baking. This course is inconvenient, because the sheath hasa large capacity for heat and its presence prolongs the time necessaryfor baking and for cooling after baking; but if the anode is so weakthat it will collapse when cold, if unsupported, it cannot be avoided.Often, however, the anode will not collapse when cold, but only when itis heated in operation. If this is so, it is preferable to support-theanode during baking with a temporary sheath of low heat capacity, easilyattached and detached, for example by means of bolts and thumbscrews.This temporary sheath need not, of course, provide cooling means. Thetemporary sheath is detached after baking, when the anode is quite cold,and replaced by the permanent cooling sheath.

I claim:-

1. In the manufacture of an evacuated electric discharge tube in whichpart of the envelope comprises a thin walled metal tube having long andshort axes and subject to collapse with elongation of its long axisunder external atmospheric pressure, the process which comprisestemporarily applying pressure at the ends of the long axis of the tubeonly for preventing elongation thereof during evacuation and thenpermanently applying continuous pressure at the ends of the long axis ofthe tube only after evacuation.

2. An evacuated electric discharge tube comprising a flattened tubularthin walled metal anode forming part of the envelope of the tube, saidanode being oval in cross section with transverse long and short axesand having walls so thin that the anode is subject to collapse underatmospheric pressure with elongation of said long axis, and a coolingsheath closely surrounding said metal anode and in pressure. engagementtherewith at opposite ends of said long axis for preventing collapse ofthe anode and elongation of said long axis under atmospheric pressure.

, 3. An evacuated electric discharge tube comprising a flattened tubularthin walled metal anode forming part of the envelope of the tube,

said anode being oval in cross section with transverse long and shortaxes and having walls so thin that the anode is subject to collapseunder atmospheric pressure. with elongation of said long axis, and acooling sheath surrounding said anode in heat conducting contacttherewith and in pressure engagement therewith at opposite ends of saidlong axis for preventing collapse of the anode and elongation of saidlong axis under atmospheric pressure.

COLIN JAMES SMI'I'HELIS.

